1. Field of the Invention
The present invention relates to an optical measurement device and a vehicle to which the optical measurement device is mounted. The optical measurement device detects the presence or absence of an object, and measures a distance from the optical measurement device to the object. The optical measurement device can be used for factory automation (FA), for security, or for automotive usage.
2. Description of the Related Art
An optical measurement device has been known which detects the presence or absence of an object, and which measures a distance to the object. As an example of the optical measurement device, the following device may be considered. Namely, the device scans a predetermined measurement field with a light beam by deflecting the light beam by a rotating polygonal mirror. The device receives the light, which is reflected by a measured object in the measurement field, with a photo detector by continuously changing a viewing angle by using the same rotating polygonal mirror, and thereby the device measures a distance to the scanning point (e.g., Patent Document 1 (Japanese Unexamined Patent Publication No. H11-304469)).
In the above-described device, a light beam from a semiconductor laser as a light source is converted into parallel light by an optical element (a transmitter lens). It is also described that a light beam is narrowed down onto a position sensitive device (PSD), which is a photo detector, by using an imaging means (a receiver lens). Although it is not explicitly described, it implies that the PSD is disposed at a position of a focal length of the receiver lens.
Namely, in these cases, a distance between an object point (the light source or the photo detector) and a lens (the transmitter lens or the receiver lens) is set to be the focal length of the lens. This setting implies that a conjugate image of the object point can be formed at infinity. In this case, however, in an angular region of each of the object points (for the projection optical system, a divergence angle of the semiconductor laser as the light source or an effective range of the transmitter lens; and for the receiving optical system, an effective range of the receiver lens), especially in the vicinity of the device, the object point is blurred, and a desired resolution may not be achieved.
There is a need for an optical measurement device which has higher angular resolution in the vicinity of the device.